The present invention relates to the field of building materials, and more particularly to a method and apparatus for producing cementitious materials designed for acoustic absorbency. The cement of the foamed cementitious composition may be a hydraulic cement including, but not limited to portland, gypsum, sorrel, slag, fly ash or calcium alumina cement. Additionally, the gypsum may include a calcium sulfate alpha hemihydrate or calcium sulfate beta hemihydrate, natural, synthetic or chemically modified calcium sulfate beta hemihydrate as well as mixtures of the above-referenced cement ingredients.
Acoustical panels for walls and ceilings provide sound absorption, aesthetics, and separate utility space in ceilings. Manufacturers strive to develop decorative acoustical wall and ceiling panels at the lowest possible cost by continuously refining the manufacturing process in an effort to reduce energy use, materials costs and waste. While cost reduction is important, there is an inherent limit to how much the process can be simplified and still produce a panel that meets the requirements of acoustical performance, moisture resistance, and fire resistance.
Typical wallboard manufacturing begins with gypsum that is mined and crushed as gypsum rock or obtained synthetically from flu gas desulfurization plants. In the calcination process, the powdered gypsum is heated to dehydrate the gypsum to a hemihydrate. The calcined gypsum or hemihydrate is known as stucco. Fillers such as perlite and fiberglass are added to the stucco to achieve the desired properties of the finished wallboard. Other additives include starch to help adhere the core to the paper face. Retarders and accelerators may be added to adjust the reaction rate. These ingredients are combined with water and soap foam in a high speed or pin mixer. Although soap foam is added to lower the core density, the resulting structure may not have sufficient porosity to be considered acoustic. The resulting mixture is placed between two sheets of paper and sized for thickness by a roller. After the core sets up, the board is cut to length then transferred to an oven to dry.
Current methods of producing acoustical ceiling panels utilize various combinations of fibers, fillers, binders, water and/or surfactants mixed into a slurry that is processed into panels. The process is very similar to the methods used in papermaking. Examples of fibers used may include mineral fiber, fiberglass, and cellulosic material. Mineral wool is a lightweight, vitreous, silica-based material spun into a fibrous structure similar to fiberglass and may also be used. Mineral wool enhances acoustical performance, fire resistance, and sag resistance of an acoustic panel.
Fillers may include expanded perlite and clay. Expanded perlite reduces material density and clay enhances fire resistance of the acoustical panel. Examples of binders used in acoustical panels may include starch, latex and/or reconstituted paper products, which link together and create a binding system that locks all of the ingredients into a structural matrix.
The above ingredients, when combined and processed appropriately, produce a porous, sound absorbent panel suitable for use as acoustic ceiling panels and other types of construction panels. Today, such panels are manufactured using very high volume processes that resemble paper production.
An aqueous cellular foam, that entrains air, forms as a result of the process of combining fibers, fillers and binders. The aqueous cellular foam eventually dries to provide a stable structure within which fiber, binders and fillers may settle and bond to create a matrix. The aqueous cellular foam mixture may include a surfactant to facilitate the entrainment of air into the mixture. The structure of a typical prior art ceiling panel material is shown in the 30xc3x97 photomicrograph of FIG. 1. The perlite particles are discemable as round nodules embedded in an interconnecting matrix of mineral wool and reconstituted newsprint fibers.
Current processes for manufacturing ceiling panels are complex, include many steps, and use large amounts of water and energy. During the process, water is progressively removed from the product through a combination of draining, pressing, and high-temperature oven heating. Some drained water may be recycled, but a majority is treated and released into the environment.
Different production processes and slurry recipes yield panels with differing acoustical and structural characteristics. There is a tradeoff between the acoustical performance and the durability. A highly porous, low-density material may exhibit the best acoustical performance. Unfortunately, a low-density material tends to be fragile and difficult to handle and exhibits low durability, low scrubability, and low tensile strength. For the purpose of this disclosure, the term durability refers to a panel""s compressive yield strength which is a measure of how easily the panel material deforms under compression. Resistance to finger indentation is an example of good compressive yield strength. Scrubability is the resistance to abrasion by repeated back and forth motion of a wet scrub brush. Tensile strength refers to the ability to lift or support a panel along one edge without the panel breaking.
Various processes and recipes are used to balance the tradeoffs inherent in the manufacture of acoustical ceiling panels. For example, one common structure for a ceiling panel is a laminate, using different layers of material, as shown in FIG. 2. One layer 201 comprises a soft, acoustically absorbent material, while the other layer 202, which faces into the room, is a more durable, sometimes structural material that is relatively transparent to sound. The acoustical performance of the panel is largely a function of layer 201, while layer 202 enhances the durability, scrubability, and aesthetics. The outer layer 202 in FIG. 2 may be a third-party supplied material. Normally, an adhesive attaches overlay 202 to layer 201. Other steps involved in the manufacture of such laminated panels include painting, cutting to size, and packaging.
Laminated panels provide a good balance between performance and durability. Such panels have the advantage of being susceptible to continuous manufacturing processing in certain steps, but require additional process steps and additional materials, e.g. the outer layer material and adhesive, which are not required when producing a homogeneous panel. Furthermore, the outer layer material usually is a high-cost constituent and the lamination process requires additional machinery, materials, and human resources. While the production of the acoustical material 201 component can typically be done in continuous fashion, the lamination step is not a continuous process. As a result, laminated panels are relatively expensive to manufacture.
Casting or molding processes are also used to create a panel structure as in FIG. 1. Casting produces a homogeneous material that is very durable and has good acoustical properties. Cast materials generally have a much higher density, and do not require an additional layer present in laminated construction. Casting is essentially a batch process in which the material is poured into a mold. The bottom of the mold is typically lined with a carrier or release agent to prevent sticking. The materials are dried in the mold, the mold is removed, and the panel undergoes a finishing process. Molded panels usually have good mechanical strength properties and exhibit good durability with acoustical performance generally not as good as a laminated panel. Drawbacks to the molding process include: the requirement of moving molds continuously throughout the process, smaller panels resulting from mold size constraints; the requirement of the added step of panel removal from the molds; and higher material cost per panel because of increased panel density.
Another common method of producing a panel having the structure shown in FIG. 1 is to extrude slurry onto a wire belt, and allow the water to drain and/or drive the water from the slurry. Other process steps include forming, drying, and surfacing or sanding resulting panels to create the desired texture in a nearly continuous process to produce an acoustically absorbent layer. Other process steps such as embossing or punching small holes into the material may further enhance the acoustical absorbency of the panel. Disadvantages include high energy costs for drying and the treating of discharge water.
With the foregoing problems in mind, there is a need to produce a low-density material for use in ceiling and other structural panels having good acoustical performance, while maintaining structural durability of the material.
Additionally, there is a need to produce a panel with high sag resistance, improved durability, a high Noise Reduction Coefficient (NRC) and a high Sound Transmission Coefficient (STC).
Furthermore there is a need to create a panel that does not require additional additives to enhance fire resistance and to create a non-homogeneous panel with a hard, high-density surface on at least one side.
The present invention provides for a process for creating an acoustically absorbent porous panel comprising the steps of dispensing dry cementitious material, dispensing fibers to create a dry mix and aqueous mixing water, surfactant and air to create a foam. Then the process provides for combining and mixing the foam and dry mix to form a foamed cementitious material comprising on a wet basis about 53% to about 68% by weight cement, about 17% to about 48% by weight water, about 0.05% to about 5% by weight fibers, and about 0.01% to about 10% by weight surfactant The foamed cementitious material is then dried or cured.
Additionally, the process provides for creating acoustical ceiling panels comprising the steps of dry mixing cement, calcium silicate and fibers in a dry mixer to create a dry mix and aqueous mixing water and surfactant in an aqueous mixer to create a diluted surfactant solution. Then combining and mixing the diluted surfactant solution, air and dry mix in a combining mixer to create a foamed cementitious material. The foamed cementitious material is then dried in a drying chamber to form an absorbent porous panel having a density between about 10 and 40 lb/ft3, a Hess rake finger scratch test result of at least 12, a Noise Reduction Coefficient of at least 0.5, and a sag test result of less than 0.15 inches at 90% RH.
Furthermore the process provides for creating acoustical ceiling panels comprising the steps of dry mixing cement and synthetic organic fibers to create a dry mix and aqueous mixing water and surfactant to create a diluted surfactant solution. Then combining and mixing the foam and dry mix to form a foamed cementitious material comprising on a wet basis about 56% to about 61% by weight cement, about 32% to about 42% by weight water, about 0.28% to about 1.3% by weight fibers, and about 0.7% to about 2% by weight surfactant. The foamed cementitious material is then dried.
The described process also includes removing the high-density skin layer from one side of a foamed cementitious panel to expose the low-density matrix for acoustical purposes. Additionally, the process may create an acoustical panel with enhanced fire resistance.
Furthermore the apparatus provides means for creating acoustical panels comprising a dispenser to convey cementitious material an aqueous mixer for aqueous mixing water and surfactant to create a diluted surfactant solution, a combining mixer for combining and mixing the foam and dry mix to form a foamed cementitious material and a dispenser to convey fibrous material. The fibrous material may be combined with the foam and cementitious material after exiting the combining mixer. In one embodiment the foamed cementitious material comprising on a wet basis about 56% to about 61% by weight cementitious material, about 32% to about 42% by weight water, about 0.28% to about 1.3% by weight fibers, and about 0.7% to about 2% by weight surfactant. The foamed cementitious material is then dried in a drying chamber.
The described apparatus also includes a sander for removing the high-density skin layer from one side of a foamed cementitious panel to expose a low-density matrix for acoustical purposes. Additionally, the apparatus may create an acoustical panel with enhanced fire resistance.
These and other features and aspects of the present invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.